The script at http://drupal.org/node/201983#comment-4483072 migrates images from Image, Image Attach, and Video Image modules to FileField in Drupal 6.

In addition to the prerequisites mentioned in the code, if you started with image.module in Drupal 5, you'll need to make sure that you've successfully upgraded image.module first. See http://drupal.org/node/342269.

For more information see http://drupal.org/node/201983